The terms "keratin" and "keratinization" are applied to substances and events of singular importance in epidermal biology. Strangely, neither has been accurately defined. The volume Keratin and Keratinization by E. H. Mercer represents the first major attempt to draw together the massive literature concerning these subjects. The resultant essays are an excellent reproduction of the complexity and confusion inherent within the material. The fault is not that of the author, whose knowledge of the subject and efforts are supreme, but rather a consequence of the subject itself.

The difficulties encountered in defining a keratin are appreciated readily by all who have considered the concept. It is clear, as the author indicates, that no one protein may be termed keratin, any more than globulin is now believed to be a discrete chemical entity. The author's conclusions that a keratin is a protein stabilized by and insolubilized by disulfide cross-linkages, and that